The present invention relates generally to displays electronic devices. More particularly, the present invention relates to a method and system for providing a wide range of colors and consistent color depth in a digital display.
Many electronic devices include functionality for providing interaction with a user via a display screen. In such devices, the display screen provides much of the information about the state of the device and is used to communicate output information to the user. Display screens typically are able to provide a greater variety and depth of information than other types of output devices (e.g., LED lights, printouts, etc.).
With modern electronic devices, the trend is to incorporate more input and output functions between the device and the user through the use of a rich visual display. One such example is the modern personal digital assistant (PDA) or cellphone. Many of these displays are using color to provide a richer user interface and to provide a richer range of output types. The most popular types of displays for such devices are LCD displays (liquid crystal display).
LCD displays are popular for, among many reasons, their small size, lightweight, and form factor (e.g., being flat). LCD displays are found in a large range of devices. Such devices include, for example, laptop computer systems, PDAs, cellphones, and the like. Color LCD displays capable of displaying a full range (or palette) of colors have proven to be very popular.
Generally, there are two basic types of LCD displays, active LCD displays and passive LCD displays. The active and passive LCD displays come in both color and black and white (e.g., gray scale) types. Active LCD displays are typically more expensive although they are capable of displaying higher intensity gray scales and colors, and are thus generally used in higher end electronic devices (e.g., laptop computers). Passive LCD displays are less expensive, and are thus more readily incorporated into a wider range of electronic devices (e.g., PDAs, cellphones, set-top boxes, etc.).
With respect to passive LCD displays, there exists a problem wherein the refresh patterns of the passive LCD display causes noticeable artifacts/interference for the user viewing the display. There are many different variables which interact with the passive LCD display to create such artifacts/interference. One such variable is interference from localized light sources. For example, typical overhead fluorescent lights (e.g., as found in many offices) tend to flicker in response to the frequency of the AC power of the building (e.g., 60 hertz). This 60 hertz flickering of the overhead lights can interfere with the refresh rate of the passive LCD display. The interference is visible in the form of a flickering of the LCD display as seen by the human eye, or by the shimmering or flashing of certain colors on the LCD display.
The problem of interference tends to limit the total number of colors and color depths the LCD is able to display. It is advantageous to implement a color display that uses a very large palette of colors and color depths, allowing the creation of very rich user interfaces and output formats. However, the refresh patterns used to create many of the different color combinations/depths cause noticeable artifacts. Some color combinations are especially prone to interference with the environmental lighting conditions.
In the prior art, device engineers have attempted to design around this problem by tuning the color combination refresh rates and the LCD display with respect to particular lighting conditions in use throughout most environments (e.g., the 60 hertz flicker rate of office overhead fluorescent lights). The many variables and characteristics affecting a particular LCD display are analyzed and designed to avoid interference problems as best as possible when used in the most common lighting environments. Unfortunately, the solution is not effective when the display is used in environments other than those to which the LCD display has been optimized, such as, for example, those environments which have lighting at frequencies other than 60 hertz, such as Europe, where lights flicker at 50 hertz.
The environmental lighting interference problem is a particular concern for passive color LCD displays. Due to the nature in which colors are generated on passive LCD displays, different colors and different color intensities on the display flicker at different frequencies. These different frequencies, in the presence of interfering environmental lights, cause certain colors of the passive LCD display to show interference artifacts. For example, certain hues and shades would appear to shimmer or flicker to a human observer. Generally speaking, this is due to the fact that with the passive color LCD displays, pixel elements are modulated in an on-off manner (turning pixel elements on and off) in order to emulate different depths of intensity. The pixel elements are turned on and off at different frequencies in order to effect different intensities. It is this nature of intensity modulation which causes particular interference problems for passive LCD displays, both color displays and gray scale displays.
For example, where overhead lights flicker at 60 hertz and a display flickers at 59 hertz, there will occur once per second an intensity xe2x80x9cpulsexe2x80x9d where the intensity of the overhead lights and the intensity of the passive LCD display will constructively interfere. This can be quite annoying to a human viewer.
Thus, the constructive and destructive interference between the environmental lighting conditions and the LCD refresh rate becomes a substantial limiter in the manner in which intensities can be modulated. In the prior art, custom intensity modulation algorithms were developed specific to environmental lighting conditions where a passive LCD display was expected to operate. The algorithms used intensity modulation schemes to yield as large a color palette as possible while avoiding those particularly observable interference patterns visible to the human eye.
However, the shortcomings of these solutions was the fact that the algorithms were specific to the lighting environment and specific to the particular type of passive LCD display. When the lighting environment changes, there is no guarantee that the annoying and observable interference patterns will not return. For example, an LCD touchscreen device being designed for lighting environments in Europe is not optimized for the lighting environments of North America. Additionally, when an electronic device is altered by using an LCD screen from a different manufacture, there would be no guarantee that the annoying and observable interference patterns would not return.
Thus, what is required is a method and system for modulating intensity of a passive LCD display which avoids the objectionable interference patterns caused by environmental lighting conditions. What is required is a solution that can readily implemented with different types of passive LCD displays from different manufacturers. What is required is a solution that is readily adaptable to different environmental lighting conditions. Additionally, the required solution should provide a large color palette while avoiding those particularly observable interference patterns visible to human eye. The present invention provides a novel solution to the above requirements.
The present invention provides a method and system for modulating intensity of a passive LCD display which avoids the objectionable interference patterns caused by environmental lighting conditions. The present invention provides a solution that can readily control different types of passive LCD displays from different manufacturers. The present invention provides a solution that is readily adaptable to different environmental lighting conditions. Additionally, the present invention provides a large color palette while avoiding those particularly observable interference patterns visible to human eye.
In one embodiment, the present invention is implemented as a method for providing intensity modulation for a display of an electronic device. The method uses tables of ratios for generating color modulation patterns. The method includes the step of defining a table of intensity values with each intensity value including a respective on-ratio and a respective off-ratio. A pixel intensity for a pixel of a display is selected by selecting a corresponding intensity value in the table. The pixel intensity is implemented by using an accumulator having an output for determining whether the pixel is on or off, wherein the pixel is on for zero and for positive values of the output and off for negative values of the output. The output is used to implement a duty cycle for the pixel, by turning the pixel on and off. The duty cycle is implemented by setting an initial output of the accumulator. The output is subsequently set to a value equal to the output minus the off-ratio if the pixel is on, and setting the output to the output plus the on-ratio if the pixel is off. Successively turning the pixel on and off in accordance with the output thereby implements a duty cycle for the pixel according to the on-ratio and off-ratio of the intensity value.
Thus, the programmable nature of the table of ratios provides a solution having a large color palette while avoiding those particularly observable interference patterns visible to human eye, and a solution that can readily control different types of passive LCD displays from different manufacturers. For example, when an electronic device is modified to use a passive LCD display from a different manufacture, hardware of the color modulator need not be altered. The ratios of the table can be readily reprogrammed to account for the characteristics of the new passive LCD display. Similarly, the table of ratios provides a solution that is readily adaptable to different environmental lighting conditions. For example, a manufacture need not produce custom versions of an electronic device for selling in different markets around the world. A global manufacturer can standardize the electronic devices, secure in the knowledge that different lighting environments in different markets around the world can be readily accounted for by reprogramming the ratios in the table.